The present invention relates to a solution for contact lenses, particularly a solution for contact lenses having an excellent cleaning effect and having an adequate safety for the eye.
Conventionally, contact lenses have been classified into water-nonabsorptive contact lenses and water-absorptive contact lenses, and classified into hard contact lenses and soft contact lenses. On each of these contact lenses, a stain of e.g. lipids (eye lipids) derived from the tear may be deposited when the lens is put on the eye in some cases, and such a stain on the lens due to the tear may cause deterioration in comfortableness in wearing or eye problems such as failure of eyesight or congestion of cornea, and accordingly it is essential to apply a cleaning treatment to a contact lens in order to safely and comfortably use the contact lens every day.
For such a cleaning treatment of a contact lens, a proper solution for contact lenses having a cleaning or removing effect over a stain is usually used. As such a solution for contact lenses, various solutions having a surfactant as a cleaning component added and incorporated therein have been proposed, and one having a nonionic surfactant such as a polyoxyalkylene block copolymer such as a polyoxyethylene-polyoxypropylene block copolymer or a derivative thereof incorporated may, for example, be known.
However, with respect to the cleaning solution for contact lenses containing such a nonionic surfactant, importance is usually attached to safety for the eye, and the concentration of the surfactant in the solution is suppressed to be as low as possible. Accordingly, with a conventional cleaning solution for contact lenses containing such a surfactant at a low concentration, no adequate cleaning power such as lipid-solubilizing power may be obtained. Accordingly, there is a fear that when a cleaning treatment of a contact lens is carried out by using such a cleaning solution, a stain of e.g. lipids tends to remain and be accumulated on the contact lens, and the eye may harmfully be influenced.
On the other hand, surfactants are classified into cationic surfactants, anionic surfactants, nonionic surfactants and ampholytic surfactants depending upon their dissociation state in their aqueous solutions. Among them, various surfactants which are classified into cationic surfactants, particularly surfactants which consist of an amino acid derivative, i.e. amino acid type cationic surfactants, have conventionally been proposed as disinfectant cleaning agents or compositions for disinfection.
For example, JP-B-51-5413 proposes a disinfectant cleaning agent to be used for disinfection and sterilization e.g. in a food sanitation field, in a field of environmental public health, in an industrial field, or in a field of agriculture and horticulture, characterized by containing, as the main component, one or at least two of amino acid type cationic surfactants having a certain structural formula. Further, JP-A-57-165305 proposes a method of blending Nxcex1-cocoyl-L-arginine ethyl esterxc2x7DL-pyrrolidone carboxylate which is an amino acid type cationic surfactant in a certain proportion with another surfactant type sterilizer such as a salt of chlorhexidine or benzalkonium chloride, so as to reinforce the effectiveness of said surfactant type sterilizer and make it possible to use the sterilizer as a sterilizer for medical use. Further, JP-A-8-183705 proposes a composition for sterilization having a strong disinfection power and being low irritative to the skin or mucous membrane, which comprises a sterilizer such as benzalkonium chloride or benzethonium chloride and Nxcex1-long chain acylarginine branched alkyl ester or its salt which is an amino acid type cationic surfactant blended, and the composition is considered to be suitable for sterilization of the skin, oral cavity and contact lenses.
As mentioned above, the amino acid type cationic surfactant is well known as a sterilization component among cationic surfactants, and in addition, it is considered to have a cleaning effect as a common property of a surfactant, since it is one type of surfactants. However, its cleaning effect, particularly an effect or performance obtainable when it is applied to contact lenses has not been well clarified so far.
Under these circumstances, the present inventors have conducted extensive studies and as a result, found that when an amino acid type cationic surfactant and a nonionic surfactant are used together, lipid-solubilizing powers of the respective surfactants are greatly improved mutually without impairing contact lenses as compared with a case where each surfactant is used alone, and that with a solution comprising an amino acid type cationic surfactant and at least one nonionic surfactant, a useful cleaning effect over a stain of lipids on a contact lens and a decrease in toxicity against the eye can be achieved simultaneously.
The present invention has been accomplished on the basis of the above discoveries, and it is an object of the present invention to provide a solution for contact lenses which is excellent in cleaning effect over a stain on a contact lens, particularly a stain of lipids without impairing the contact lens, and which secures adequate safety for the eye.
According to the present invention, there is provided a solution for contact lenses which comprises an amino acid type cationic surfactant and at least one nonionic surfactant.
Now, the present invention will be described in detail with reference to the preferred embodiments.